2-NAS project?

Further to my previous message I would like to purchase and install the following NAS configuration:
NAS-1 UK, Back-up, File server, Media server for 3 Macs, 2 iPads, 4 iPhones, 1 Apple TV etc - Synology DS 1520+ ?
NAS-2 GR, Off-site back-up, Media server for 2 Macs etc - Synology DS220+ ?
Current total net storage requirement ~5TB, expected to increase to 7 TB within 2 years
My questions:
- Is the choice of DS correct? - how much RAM, NVMe and HDD capacity should I go for?
- will syncing between the two NAS work even though my ISPs in UK and Greece will not provide me fixed IP addresses

Yes, DS1520+ is their biggest NAS with a multimedia chip built inside. Having 4 CPU cores do help with multitasking. Adding NVMe cache might not be something you need in-home environment. This helps with virtual machines, web servers and 10+ user environments accessing the same data so often.Having more RAM would also benefit only in the situations above. You need to utilise RAM to get the speed boost.Regarding hard drives, you could start with 3 or 4 drives and add more drive later. SHR1 with 3TB drives would give around 7TB storage space.DS220+ is a dual-core version of it. It is still an upgradable model with decent performance. It would do a good job serving as a multimedia server for fewer users.Connecting.The public IP would need to be static, or use DDNS or DynDNS, or a VPN. Those will be the only options.Here are some instructions on DDNS:https://www.synology.com/en-global/knowledgebase/DSM/help/DSM/AdminCenter/connection_ddnshttps://www.synology.com/en-uk/knowledgebase/DSM/tutorial/Network/Frequently_asked_questions_about_DDNSIf you choose to link both NAS via VPN you will need to create a VPN server and connect other NAS as a clientDYNDNS- https://youtu.be/mF6wa8Ej4fQ?t=577https://account.dyn.com/I hope this helps.